The overall objective of our research is to study the role of sensory influences originating from the upper airway on respiratory control in health and disease. We propose to continue studies on laryngeal afferents and reflexes in anesthetized spontaneously breathing adult dogs. In addition, developmental changes in upper airway functions will be studied in a neonatal dog model. Action potentials from single fibers of the superior laryngeal nerve and/or electromyogram of various upper airway muscles will be monitored together with esophageal pressure and laryngeal temperature in most studies. Their are five main objectives: 1) To elucidate the mechanism involved in reflex responses elicited by airflow through the upper airway. the proposed research should establish that either laryngeal mechanoreceptor inhibitor or cold receptor stimulation or both are responsible for the ventilatory depression observed during airflow through the upper airway in neonates, 2) To determine developmental changes in the effects of intralaryngeal CO2 on breathing pattern. A greater reflex inhibition of breathing by CO2 is predicted in neonates. 3) To determine the afferent pathway and characterize the response of afferent nerve endings mediating the bronchospasm observed during high frequency pressure oscillations in the upper airway, 4) To investigate the influences of changes in airway surface liquid composition and osmolality on the response of laryngeal afferents and characterize further the behavior of rapidly adapting laryngeal endings, 5) To determine the relative contribution of various upper airway muscle groups in the maintenance of upper airway patency. These studies should provide new information on the processes involved in upper airway maintenance and may clarify our understanding of the pathophysiology of obstructive sleep apnea, neonatal apnea and sudden infant death syndrome.